Spark plug



Ma'rch 26, 1935.

r @gj RABEzzANA SPARK PLUG Filed oct. 2, 1955 'linnn 4 g4 @M www Patented Mar. 26, 1935 UNITED STATES,

PATENT OFFICE SPARK PLUG Ware Application october 2, 1933, serial No. 691,763

4 Claims.

` ing member whereby the latter is less'likely to be broken or otherwise injured during the as sembling of the central lelectrode therewith, and the securing it in place in the passage aforesaid, and is subjected to less strain and possible injury when the plug is in use than has heretofore commonly been the case in spark plug insulators.

A further object of my invention is to provide a spark plug with insulating member and central electrode features whereby such expansion of the electrode as occurs when the plug is in use, due to the heating thereof by burning gases within the engine cylinder, will be less likely to injure the insulating member as by cracking the same, or by setting up stresses therein tending to crack or otherwise injure it, than has heretofore been the case in spark' plugs; and a still further object of my invention is to provide central electrode and insulating member features whereby heat communicated to the electrode bythe burning gases will be more rapidly and eiiectively conducted to the insulating member and to the shell of the plug and the surrounding atmosphereI than has yheretoforecommonly been the case.

With the above and other objects of invention in view my invention consists in the improved central electrode and insulating member features illustrated in the accompanying drawing, described in the following specification, and particularlyclaimed at the end thereof; and in such variations and modifications thereof, within the scope of the concluding claims, as will be obvious to those skilled in the art to which my invention relates.

In the drawing wherein the preferred form of my invention is illustrated:

Figure 1 is a view showing a section upon a longitudinally extending central plane, of a spark plug having electrode and insulating member features in accordance with my invention.

Figure 2 is a similar view showing slight variations of various of the features of my invention.

Figure 3 is a fragmentary sectional view upon (Cl. 12S-169) a transverse plane indicated by the line 3 3, Figure 2, upon a larger scale.

Figure 4 is a sectional view similar to Figures 1 and 2, but showing a modied form of my invention. ,j

Figure 5 is a view showing the central part of the central electrode of Figure 4 in elevation and upon a larger scale.

Referring to the drawing, the reference numeral designates the external metallic shell of a spark plug, which as usual is threaded to screw into a similarly threaded opening in an internal combustion engine cylinder head; and within this shell orl casing is an insulating member l1, the same being shown as of the type having an enlarged central portion resting upon a ledge 12 of the casing, and as secured within the same by an inwardly bent holding ilange 13. My invention, however, is not limited to any particular form of insulating member, nor to the scheme illustrated for securing the same Within the external shell of the plug.

The insulating member has a longitudinally ex tending passage extending through it, the same being of lesser diameter at its lower part 14 than at its upper part l5, whereby an internal supporting ledge 16 is provided; said ledge being preferably located within the enlarged central portion of the insulating member. The central electrode has a larger outer or upper part 17 extending through the passage 15, a smaller inner arid lower part 18 which extends through the passage 14, and an intermediate shoulder 19 which engages the ledge 16 when the central electrode is assembled with the insulating member.

The central electrode is a unitary single piece structure although it is commonly made in two parts joined together adjacent the shoulder 19, because the inner part is commonly made of a more expensive metal (in order to endure the high temperature met with when the plug is in use) than is necessary in the outer part, which is less highly heated and is not subjected to the action of the spark gap. The inner part 18 extends loosely through the passage 14 (that is, it is not cemented in place therein) so that the same may expand independently of the insulating member and without subjecting the latter to strain tending to break it, as the two are heated when the plug is in use. The outer end 17, however, is cemented in place within the passage 15 to secure the requisite gas-tight and non-leaking qualities necessary in a. spark plug. 'I'he central electrode fits quite loosely within the passages through which it extends so that it,y may be readily but in place without binding in the passages provided for it, so that the insulating member will not be broken or strained during the assembling of the parts; the requisite gas tightness 4of the plug being secured by cement which lls the interstices between the parts as next appears.

The upper part 17 of the central electrode is of hollow tubular form, as shown, and holes 20 are provided adjacent the lower end of this part and above the ledge 16 and shoulder 19 through which cement 2l (which is supplied under pressure through the electrode passage) may ow therethrough and through the holes and ll the interstices between said upper part and the interior of the passage l through which it extends.

In Figure 1 the interior of the passage l5 is threaded as is likewise the upper end of the part 17 of the electrode, the threads thus providing roughness to secure a more iirm holding action of the cement 21. In all forms the threaded part which is above the upper extremity of the insulating member provides for holding nuts -or other forms of terminal connector, for securing a supply conductor the plug, as will be understood.

In the form of my invention illustrated in Figure 2 the threads upon the upper electrode part 17 are large enough in diameter to engage loosely with the threads within the passage 15, so as to provide positive locking of the electrode in place within the insulator passage, and the interstices between the parts are lled with cement as in the Figure l form to secure gas tight sealing about the electrode. In the form illustrated in Figure 1 the lower portion 18 of the central electrode is welded to the upper part at 22, whereasv in the form illustrated in Figure 2 the two parts are secured together by forcing portions of the wall of the upper part, at its lower end, into holding engagement with the upper end of the lower part 18, as in the familiar staking method, and as shown at 23.

In the form of my invention illustrated in Figures 4 and 5 lugs'24 are formed at the lower end` of the upper part of the central electrode by swaging, or equivalent forming process, and these engage loosely with a coarse internal thread 25 within and at the lower end of the larger outer passage in the insulating membergll; the interstices between the parts being filled with cement as in the other forms described. This permits a rapid assembling of the central electrode preliminarily to the cementing step; and the location of the interlocking elements close to the ledge 16 and shoulder 19 provides a structure wherein the engaging parts (the coarsely threaded part and the part having the lugs' 24) being short, differential expansion of the metallic electrode and the insulating member will have little or no effect as regards loosening of the joint between the two.

The threaded parts of the forms illustrated in Figures 1 and 2 may likewise be adjacent the lower ends of the central electrode and the inner ends of the larger outer passages in the insulating member, with the same result in re'ducing the lengths of the interlocking engagement between the insulating member and the electrode to a minimum and thus avoiding entirely, or substantially so, the loosening effect of dierential expansion when the plug becomes heated; and in all forms of my invention the filling of the space between the central electrode and the passage above the ledge 16 and shoulder 19 through which it eX- images tends provide for a rapid flow of heat from the central electrode to the insulating member and to the surrounding atmosphere.

Having thus described and explained my invention I claim` and desire to secure by Letters Patent:

1. In a spark plug, an insulating member having an internal ledge intermediate its ends, a passage leading from said ledge to the inner end of said insulating member, and a larger passage leading from said ledge to the outer end of said insulating member; and an electrode extending through both said passages and having a shoulder which rests upon the ledge aforesaid, and the upper part only of which electrode iscemented in place within the larger passage in said insulating member; the upper part of said electrode being tubular in form, and smaller than the passage through which it extends, and the wall thereof having a hole adjacent its lowerend.

2. In a spark'plug, an insulating member having an internal ledge intermediate its ends, a passage leading from said ledge to the inner end of said insulating member, and a larger passage leading from said ledge to the outer endv of said insulating member; an electrode extending through both said passages and having a shoulder which rests upon the ledge aforesaid, the upper part of said electrode being tubular in form, and smaller than the passage through which it extends, and the wall thereof having a hole adjacent said ledge and said shoulder; interlocking elementsI upon said electrode and within the larger passage aforesaid for holding said electrode in place within the passages through which it extends; and cement filling the interstices between the upper part of said electrode and the larger upper passage within which it lies.

3. In a spark plug, an insulating member having an internal ledge intermediate its ends, a passage leading from said ledge to the inner end of said' insulating member, and a larger passage leading from said ledge to the outer end of said insulating member; and an electrode extending through both said passages and having a shoulder which rests upon the ledge aforesaid, and the upper part only of which electrode is cemented in place within the larger passage in said insulating member; the upper part of said electrode being tubular in form, and smaller than the passage through which it extends, and the wall thereof having a hole adjacent said ledge and said shoulder.

4. In a spark plug, an insulating member having an internal ledge intermediate its ends, a passage leadingwfrorn said ledge to the innerend of said insulating member, and a larger passage leading from said ledge to the out/er end of said insulating member; an electrode extending through both said passages and having a shoulder which rests upon said ledge, and the upper part only of which electrode is cemented in place within the larger of the passages aforesaid, the upper part of said electrode being tubular in form and smaller than the passagethrough which it extends and the wall thereof having a hole adjacent its lower end; and interlocking elements upon said electrode and within the larger passage aforesaid, said elements being located adjacent the lower ends of said larger passage and the upper tubular part of said electrode.

moron RABEZZANA. 

